Surface gap spark plug and rotary engine combination

ABSTRACT

A surface gap type spark plug in combination with a rotary engine having an ignition opening in the housing inner surface, the opening being substantially entirely closed off by the firing end of the plug to substantially eliminate any blow-by or leakage gas as the apex seal wipes over the opening area, the reach of the plug being precisely controlled to place the sparking surface of the plug at the housing inner surface with the spark substantially in the combustion chamber while precluding projection of the plug into the combustion space beyond the inner housing surface, the closing of the ignition opening at the housing inner surface serving also to preclude collection of lubricant.

United States Patent [191 Paxton et a1.

[45 1 Aug. 27, 1974 SURFACE GAP SPARK PLUG AND ROTARY ENGINE COMBINATION Inventors: Wayne E. Paxton, Flint; Edward A.

Rishavy, Warren; James II. Currie, Rochester, all of Mich.

General Motors Corporation, Detroit, Mich.

Filed: July 2, 1973 Appl. No.: 375,369

[73] Assignee:

US. Cl 123/839, 123/169 R, 313/143 Int. Cl. F02b 53/12 Field of Search 123/809, 8.45, 169 CL,

123/169 C, 169 E, 169 R; 313/118, 143

References Cited UNITED STATES PATENTS Beaubier 313/143 X Burley l23/8.45 X

Jones et a1. 123/169 R Primary Examiner-William L. Freeh Assistant Examiner-Michael Koczo, Jr. Attorney, Agent, or Firm-Sidney Carter.

[ ABSTRACT A surface gap type spark plug in combination with a rotary engine having an ignition opening in the housing inner surface, the opening being substantially entirely closed off by the firing end of the plug to substantially eliminate any blow-by or leakage gas as the apex seal wipes over the opening area, the reach of V the plug being precisely controlled to place the sparking surface of the plug at the housing inner surface with the spark substantially in the combustion chamber while precluding projection of the plug into the combustion space beyond the inner housing surface, the closing of the ignition opening at the housing inner surface serving also to preclude collection of lubricant.

3 Claims, 3 Drawing Figures SURFACE GAP SPARK PLUG AND ROTARY ENGINE COMBINATION One of the principal goals in the design of rotary type engines is that of developing a system in which combustion is as complete as possible to minimize the presence of unburned hydrocarbons in the exhaust. This indicates the need for the elimination of misfiring for the full and effective use of sparking energy and for the elimination of pockets which can permit blow-by or leakage gas and accumulation of lubricant which can cause plug fouling and high oil usage.

As is shown by US. Pat. No. 3,597,648 issued Aug. 3, 1971 to M. Shibagaki and I. Ogasawara and US. Pat. No. 3,719,850 issued Mar. 6, 1973 to Manfred Schafer, various spark plug-rotary engine combinations have been proposed. However, as shown, each has presented cavities which serve as pockets enabling blow-by or leakage gas and accumulation of lubricant, each has used a soft metal or crushable gasket between matching flat, planar seating surfaces on the plug shell and housing to obtain a gas-tight seal therebetween thus preeluding precise location of the end of the plug at the inner surface of the housing, and each locates the sparking end 'of the plug a relatively substantial distance back from the inner surface of the housing thus precluding full and'direct use of the sparking energy since the spark isin a cavity rather than at the inner housing surface.

Similarly, while surface gap spark plugs have been used in rotary engines for such low power devices as snowmobiles, the engine-plug seal is of the flat soft or crushable type noted above with the result that location of the sparking end of the plug is imprecise and the combination must necessarily be designed to assure that the end is well within the spark plug bore and relatively substantially back from the inner surface of the housing. Also, though the use of conical sealing surfaces was disclosed in SAE publication 67.0148 entitled Development of a New Automotive Spark Plug" and was presented at Jan. 9-13, I967, the disclosure covers the standard automotive side wire electrode type having the spark gap located within the top of the combustion chamber, the main feature being the reduction in diameter of shell made possible by the new design.

It is an object of our invention to provide an improved rotary engine-surface gap spark plug combination wherein the surface gap is precisely located at the inner surface of the housing and substantially cmpletely closes the ignition opening in the surface.

It is a further object of our invention to provide an ignition opening and adjacent bore portion which is substantially smaller indiameter than the remaining portions of the bore in the housing.

It is a still further object of our invention to provide an enginesurface gap spark plug combination wherein an SAE Congress in Detroit, Mich,

2 FIG. 2 is an end view of FIG. 1 taken on line 2-2;

FIG. 3 is a sectional view of the surface gap spark plug along its axis.

As shown in FIG. 1, the combination of our invention comprises a housing 1 having an outer surface 3 and an inner surface 5, the inner surface defining a trochoidal chamber in which a rotor member is positioned for rotary movement with respect thereto and in sealing contact therewith in the manner well known in the art. A bore 7 is provided in the housing 1 extending from the outer to the inner surface and forming an ignition opening 9 on the inner surface.

Intermediate the ends of the bore 7 and forming a portion of the wall of the bore is a threaded section 11 for the removable installation of the spark plug 13 having correspondingly formed threads 15 on a portion of shell 17. While the preferred embodiment of our invention asshown and described provides a threaded installation of the plug 13 within bore 7, it is to be understood that other means well known in the art, such as a flanged and bolted interconnection, may also be used.

Also provided within the bore 7 as a part of its wall surface is a conical sealing surface 19 which is formed to converge toward the inner surface 5 with its axis sub stantially coincident with the axisof the bore. As is 7 shown in FIGS. 1 and 3, shell 17 is provided with a corthe plane of the end of the plug is substantially tangent to the extended inner surface of the ignition opening.

respondingly formed conical sealing surfaceZl which makes direct surface-to-surface contact with conical sealing surface 19 formed in the wall of bore 7 to form a gas-tight seal upon threading the plug 13 into the bore. The direct surface-to-surface contactserves to precisely locatethe plane 18 0f the end of the shell 17 as close as possible to the ignition opening 9 while precluding any portion of the end of the plug 13 extending beyond the inner surface 5. In the design of the plug 13,

both the sparking end 23 of the centerwire 25 and the lower end 27 of the insulator 29 are dimensioned so as to be positioned back from the plane 18 of the end of the shell while being closely adjacent thereto.

Also as shown in FIGS. 1 and 3, the end 31 of the shell 17 adjacent to the firing end 23 of the center electrode 25 forms an annular ground electrode 33, the space between the two electrodes being substantially filled by the lower end 27 of the insulator to eliminate any pocket within the end of the plug 13. The elimination of any pocket within the ignition opening is further assured by designing the end '31v of the shell to substantially fill the ignition opening 9. More particularly, as shown, the lower end 8 of the bore 7 is cylindrical in shape with the end 31 of the shell correspondingly shaped and of substantially the same diameter as that of the bore end 8. While the lower end 8 of the bore is cylindrical in form, it is of course possible to use other shapes, e.g., conical, the end 31 of the shell being then correspondingly shaped and dimensioned. As may be seen from the drawing, the lower end 8 of the bore 7 is appreciably smaller than the upper portions of the bore in order to enable as small an ignition opening as possible. Similarly. in order to locate the plane 18 of the end of the shell as close to the inner surface 5 as possible, the plug 13 is so dimensioned in reach with respect to the conical sealing surfaces as to locate the plane 8 substantially tangent to the extended inner surface 5 at the center of the ignition opening 9.

With reference to the design of the preferred embodiment of the spark plug 13 as shown in FIG. 3, the insulator 29 is positioned in gas-tight relationship in shell 17 by means of an upper sealing gasket 35, the lower sealing shoulder 37 on the insulator being glazed and forming a seal with the correspondingly positioned shoulder 39 formed on the inner surface of the shell 17. A lower sealing gasket may of course be used in lieu of the glazed surface seal. The upper end 41 of the center electrode 25 is sealed in gas-tight relationship in the centerbore 43 by means of a conducting glass and resistor seal combination as is well known in the art, such as the combination disclosed in the patent to Achey US. Pat. No. 3,538,02l Resistor Composition, dated Nov. 3, 1970..

The series gap design provided in the upper portion of the centerbore 43 is of the type disclosed in assignees copending application Ser. No. 267,090 filed June 28, 1972, Series Gap Spark Plug," Vaillancour et al. With specific reference to FIG. 3, the terminal screw 45 is formed with a cap-like flange 47 which is positioned on the upper end surface of the insulator 29. Since the insulator end surface is rough, an air vent path from the auxiliary spark gap is provided between the flange-47 and the insulator end surface. As shown, terminal screw 45 is retained on the insulator end surface by means of retainer ring 49 which is magnaformed, rolled or otherwiseworked to clamp around the top rib 51 formed on the upper end of the insulator and onto the upper surface of the cap-like flange 47. The air path from the auxiliary spark gap is completed by providing a plurality of vent grooves 53 on the inner surface of the retainer ring 49 from the top edge thereof down toward the insulator top end surface. Also as shown, a metal spacer 55 is provided in the centerbore to define the other end of auxiliary spark gap with the inner end of the terminal screw.

As is clear from the foregoing description, we have provided a spark plug-rotary engine housing combination which enables maximum efficiency of spark plug operation while minimizing any ignition opening cavity which would serve to permit blow-by of combustion gases, collection of lubricant and increased unburned hydrocarbons in the exhaust gases. As used in describing the features of our invention, the term substantially" is intended to encompass manufacturing tolerances within the skill of the art. The features of our novel combination are as set forth in the claims which follow.

' What is claimed is:

1. In combination in a rotary engine, a housing having an inner surface defining a trochoidal chamber adapted to have a rotor member positioned therein for rotary movement with respect thereto and in sealing contact therewith, a bore provided in said housing from the outer surface to said inner surface thereof and forming an ignition opening on said inner surface, said bore having a threaded section provided therein intermediate its ends, a conical sealing surface provided in the wall of said bore intermediate its ends and converging toward said inner surface and having its axis substantially coincident with the axis of said bore, a surface gap type spark plug secured within said bore in gas-tight relationship with said housing, said spark plug comprising a ceramic insulator having a centerbore therethrough, a center electrode within the lower end of said centerbore, the end of said center electrode opposite its firing end being sealed in gas-tight relationship with the wall of said centerbore, a terminal screw positioned within the upper end of said centerbore'and adapted to pass electrical energy through to said centerwire, a metal shell positioned about said insulator in gas-tight relationship therewith, a threaded portion being provided on the surface of said shell and cooperating with said threaded section provided in said bore to retain said spark plug .within said bore, a conical sealing surface on the surface of said shell in direct surface-to-surface contact with said correspondingly formed conical sealing surface in said bore to form a gas-tight seal therewith, the end of said shell adjacent the firing end of said center electrode constituting an annular ground electrode and being correspondingly shaped to the shape of the end portion of said bore adjacent said ignition opening and being substantially of the same size in order to substantially completely close said ignition opening, and of said insulator separating and substantially filling the annular space between the electrodes to form a surface spark gap therebetween, and both the sparking end of the center electrode and the lower end of said insulator being positioned back from the plane of the end of said shell, said direct surface-to-surface sealing contact serving to precisely locate said plane as closely as possible to said ignition opening while precluding any portion of the end of said spark plug extending beyond said inner surface of said housing.

2. The combination as set forth in claim 1 wherein the end portion of said bore adjacent said ignition opening is cylindrical and is appreciably smaller in diameter than the remaining portions of said bore.

3. The combination as set forth in claim 2 wherein said plane is substantially tangent to the extended inner surface of said housing at the center of said ignition opening. 

1. In combination in a rotary engine, a housing having an inner surface defining a trochoidal chamber adapted to have a rotor member positioned therein for rotary movement with respect thereto and in sealing contact therewith, a bore provided in said housing from the outer surface to said inner surface thereof and forming an ignition opening on said inner surface, said bore having a threaded section provided therein intermediate its ends, a conical sealing surface provided in the wall of said bore intermediate its ends and converging toward said inner surface and having its axis substantially coincident with the axis of said bore, a surface gap type spark plug secured within said bore in gas-tight relationship with said housing, said spark plug comprising a ceramic insulator having a centerbore therethrough, a center electrode within the lower end of said centerbore, the end of said center electrode opposite its firing end being sealed in gas-tight relationship with the wall of said centerbore, a terminal screw positioned within the upper end of said centerbore and adapted to pass electrical energy through to said centerwire, a metal shell positioned about said insulator in gas-tight reLationship therewith, a threaded portion being provided on the surface of said shell and cooperating with said threaded section provided in said bore to retain said spark plug within said bore, a conical sealing surface on the surface of said shell in direct surface-to-surface contact with said correspondingly formed conical sealing surface in said bore to form a gas-tight seal therewith, the end of said shell adjacent the firing end of said center electrode constituting an annular ground electrode and being correspondingly shaped to the shape of the end portion of said bore adjacent said ignition opening and being substantially of the same size in order to substantially completely close said ignition opening, and of said insulator separating and substantially filling the annular space between the electrodes to form a surface spark gap therebetween, and both the sparking end of the center electrode and the lower end of said insulator being positioned back from the plane of the end of said shell, said direct surface-to-surface sealing contact serving to precisely locate said plane as closely as possible to said ignition opening while precluding any portion of the end of said spark plug extending beyond said inner surface of said housing.
 2. The combination as set forth in claim 1 wherein the end portion of said bore adjacent said ignition opening is cylindrical and is appreciably smaller in diameter than the remaining portions of said bore.
 3. The combination as set forth in claim 2 wherein said plane is substantially tangent to the extended inner surface of said housing at the center of said ignition opening. 